Flloor insulation between timber joists.

[pep411]

Hi,

I am planning to lift the existing floor boards. I want to insulate the downstairs lounge, dining room and hallway.

The idea is to friction fix polystyrene boards 100mm between joists. I will get support under the joists to hold the insulation, just in case.

I will be avoiding all PVC wires but where unavoidable, I will be using Celotex GA 4090 90mm. Cannot afford using celotex all throughout. The area downstairs is 60m2.

All the CH pipes will be insulated and air brick left unobstructed.

Instead of replacing the floor boards, I want to screw fix 18mm (8X4) plywood. The we will be install solid wood floor.

What do you think about my idea.

 

[HERTS P&D]

I went to a property 2 weeks ago that had done the same. They even fitted ply sheeting to the floor and tiled it.

Then when they had a burst pipe it took a lot of work just to get to the pipe work. Causing a lot of damage.

Andy

 

[pep411]

Just had brand new central heating pipes installed as old boiler was gravity fed boiler with copper pipes.

The pipes are white plastic ones. Yes it will be a nightmare to get to the pipes, but then how often. Sod's law applicable in any scenario.

 

[freddiemercurystwin]

I went to a property 2 weeks ago that had done the same. They even fitted ply sheeting to the floor and tiled it.

Then when they had a burst pipe it took a lot of work just to get to the pipe work. Causing a lot of damage.

Andy

Thanks for taking part!

@ the OP your plan sounds fine may aswell just use 100 poly all over or even thicker if funds permit. Make sure its held up with battens or nails into the joists and is hard up against the underside of the boards. Seal any gap with expanding foam..

We assume your ventilation beneath the floor is adequate.

 

[pep411]

Thanks freddy. The void below is metre deep. What did u actual mean by adequate ventilation.

Do I need dpm above or below insulation.

If i use polystyrene all over. How can i get around degradation of pvc wires by polystyrene.

 

[freddiemercurystwin]

Ahh sorry my bad, didn't notice your earlier reference to pvc degradation, there is extensive evidence that pvc wiring can be degraded and ought to be de-rated when in contact with polystyrene.

Unless you can cut some channels or voids in the insulation then Celotex may be necessary. If your wiring is right under your boards you may get away with just a 25mm layer of Celotex and then your polystyrene under that.

Regarding ventilation if there are a couple of air bricks either side of your house and they are clear then that will probably be fine. No need for any kind of dpm under or above the insulation.

 

[pep411]

We have just started taking up the lounge floor boards. My idea of using Celotex nearer to PVC wires is proving very expensire. There is plethora of wires underneath. TV dual cables, electric cables, cat data cables, home theatre cables.

This issue is only with lounge which is extended from original property and void is just around 20 cm from below the joists.

Is it worth insulating the shallow part of property. The void under dinning room and hallway is metre deep.

 

[freddiemercurystwin]

Is it worth insulating the shallow part of property. The void under dinning room and hallway is metre deep.

Not sure I follow?

With regards to the degradation of PVC wiring I am afraid I am a little out of my depth, unless anyone else pipes up I suggest you start a thread in the Electrics section.

 

[JohnD]

is it too late for you to change to fibreglass loft rolls?

you tack garden netting to the joists to stop it falling out.

You can do it from above if you are taking the floorboards up.